1. Field of the Invention
The invention relates to a low standby power circuit used in a pointing device, such as might be used in a locator system.
2. Related Art
Locator systems, such as those available from Luidia, Inc., of San Carlos, California, the assignee of the present invention, include a pointing device capable of being moved about, and a matching device for detecting the position of the pointing device by signals sent from one device to the other. The device made by Luidia includes a transmitter in the pointing device, and one or more receivers capable of receiving signals from the transmitter and interpreting the location of the transmitter in response to those signals. In the remainder of the discussion, such a configuration will be assumed, although those in the art will understand that the inventive aspects may also be applied to a system wherein the pointing device receives signals from one or more matching devices to determine the location.
As an example, the pointing device containing the transmitter might be shaped like a marker pen or other drawing tool (sometimes called a “transmitter pen”) with the matching device (the receiver(s)) deriving the location of the pointing device on a planar surface (sometimes called an “active area” in which position detection might occur), e.g., in response to signals from the transmitter in the pointing devices. In such systems, the matching device, e.g., receiver might send signals to a display, or to another communication or computing system, with the effect that movement of the transmitter pen would have the effect of drawing or writing on both the active area and also in storage in the connected device, and/or displayed on a display system. When the active area itself includes a projection screen used with a display projector coupled to the connected device, the transmitter pen need not have any actual ink or other marking material, as the drawing can be done by using the display projector to show annotations on the screen.
A first problem with known systems is that the pointing device, e.g., transmitter pen includes electronic circuitry, e.g., circuitry capable of transmitting signals to the matching device, e.g., receiver(s), with the effect that the pointing device consumes electrical power. The electrical power for the pointing device might be supplied from a battery, but this has the drawbacks (1) that the electrical power would be wasted while the pointing device is not in active use, and (2) that the battery would eventually have to be replaced or recharged.
Although some known systems, such as for example computer monitors, do include circuitry for operating in a reduced-power mode when relatively inactive, such known systems are subject to several drawbacks as well as follows:
(1) Circuitry for operating in a reduced-power mode under selected conditions is more complex and often more expensive than circuitry without that capability.
(2) Even operating in a reduced-power mode, such known circuitry typically uses an amount of power that is more than insignificant, albeit much lower than would be used in a regular operational mode, with the effect that the reduced-power mode does waste at least some power and can eventually cause the battery to be replaced or recharged.
(3) Known circuitry for operating in a reduced-power mode still involves supplying power for the reduced-power mode, with this power involving more than the voltage supplied by a battery. For example, many microelectronic circuits operate at voltages such as 3.3 volts or 5.0 volts, even in reduced-power mode, while non-lithium based battery power is lower than that, e.g., only 1.5 volts using a carbon-zinc battery. Such known circuitry accordingly involves a DC-to-DC converter between the battery and the voltage used by the microelectronic circuit, and the DC-to-DC converter itself draws an amount of power that is more than insignificant, with the effect that the battery can be drained relatively rapidly even when the reduced-power mode for the microelectronic circuit is quite efficient.
(4) Known circuitry for operating in a reduced power mode with DC-to-DC converter involved can only transition from an inactive state to an active state from a single source. e.g., the function switch or power switch.
(5) Known circuitry for operating in a reduced-power mode often involves a delay in fully operational capability, sometimes called warm-up time, during which the circuitry might fail to operate as it would have if fully on at all times.
A pointing device, e.g., transmitter pen might have more than one way to transition from its inactive state to an active state, with the effect that it would be advantageous to provide, with any transition from a no-power mode to a powered mode, information regarding which way that transition was triggered, such as for example which one of a set of passive sensors was invoked to cause the transition. In locator systems including a pointing device, e.g., transmitter pen and a mechanism to make an area active for position detection, e.g. one or more receivers (such as those available from Luidia), the pointing device, e.g., transmitter pen might include a first sensor capable of detecting when the pointing device is touched to the active area for writing, and one or more additional sensors capable of activating other features. In one embodiment, these additional sensors can operate in a manner similar to mouse buttons. These additional sensors might alternatively be used with the effect of adjusting the characteristics of the display in the case that the positions detected are displayed, such as for example the color of a displayed line, whether a displayed line is dashed or dotted or not, and the like.
Known circuitry for operating in a reduced-power mode does not provide both (1) a state in which essentially no power is used (a “no-power” state), and (2) any substantial information, when transitioning to an active state from that no-power state, about passive sensors that might have been triggered while in that no-power state. This has the effect that if there is more than one way to transition to active state, circuitry that is transitioned to the active state does not have any convenient way to tell which way that transition was triggered.
For example, with known circuitry for operating in a reduced-power mode, if there are multiple buttons or switches (or other types of sensors) to turn the power on, either (1) the known circuitry involves an amount of power drain so that the known circuitry can detect which one was used to turn the power on, or (2) the known circuitry does not know which one of the multiple buttons or switches was used to turn the power on. In some known circuitry, either (A) the power drain is from the DC-to-DC converter stays on, for the purpose of providing power to a microcontroller, so the microcontroller can detect which switch was used to turn the power on, or (B) the power drain is from the microcontroller itself, which stays on in a reduced-power mode, using a higher-voltage source than a 1.5 volt battery, for the purpose of detecting which switch was used to turn the power on.
Accordingly, it would be advantageous to provide a technique providing substantially no power consumption in a relatively inactive state, while also providing a substantially immediate indicator of the cause of a transition to an active state when power is provided.